(Updates with more comment from Lavrov, and a South Korean foreign ministry spokesperson)
By Soo-hyang Choi
SEOUL, Oct 19 (Reuters) - Russian Foreign Minister Sergei Lavrov thanked North Korea for backing his country's military actions in Ukraine and pledged Moscow's «complete support and solidarity» for North Korean leader Kim Jong Un, Russia's foreign ministry said.
Lavrov arrived in Pyongyang on Wednesday for meetings seen as setting the stage for a visit by President Vladimir Putin, who has stepped up cooperation with politically isolated North Korea.
Speaking at a reception hosted by the North on Wednesday, Lavrov said Moscow strongly valued Pyongyang's «unwavering and principled support» for Russia in the Ukraine war, which it calls a «special military operation».
«Likewise the Russian Federation extends its complete support and solidarity with the aspirations of the DPRK,» Lavrov said, according to the transcript of the speech released on his ministry's website. DPRK are the initials of the North's official name, the Democratic People's Republic of Korea.
After talks with North Korean Foreign Minister Choe Son Hui, Lavrov later told reporters that increased military activities by the United States and its allies Japan and South Korea were a cause for concern, Russia's state-run RIA news agency reported.
The U.S. and South Korean navies on Thursday joined those of four other countries - Canada, Belgium, New Zealand and the Philippines - for an anti-naval mine exercise off South Korea's south coast, the South Korean defence ministry said.
In his comments, Lavrov said North Korea, China and Russia were pursuing a policy of seeking to ease regional tensions.
North Korean state media said Lavrov's visit would mark a «significant occasion» in further consolidating relations between Pyongyang and Moscow.
Photos released by the Russian foreign ministry showed Lavrov being greeted by people holding flowers and flags of the two countries upon arrival.
Lavrov's two-day visit comes a month after North Korean leader Kim made a rare trip to Russia, during which he invited Putin to Pyongyang and discussed military cooperation.
This week's visit will offer a «valuable opportunity» to review and outline practical steps for the implementation of the agreements reached between the two leaders, Lavrov said.
Russia's TASS news agency said Lavrov might also brief North Korean leaders on the results of Putin's visit this week to China.
A U.S. think-tank said on Tuesday that satellite images showed continued activity around a North Korean port near Russia, indicating at least six trips by sea between the two countries since late August.
The shipments between the port of Rajin and Russia's Dunai are possibly related to the transfer of North Korean munitions to Russia, the Washington-based Center for Strategic and International Studies (CSIS) said.
Separately, a North Korean cargo-passenger ferry that had carried foreign tourists from Japan or South Korea was seen at a drydock at the same port this month, most likely for maintenance, CSIS said.
It was not clear whether the vessel would be used to supplement trade activity between Russia and North Korea, it said.
The White House said last week that North Korea had recently provided Russia with a shipment of weapons in what it called a troubling development.
Kremlin spokesman Dmitry Peskov said the Western allegations were not based on evidence.
South Korea and the United States have expressed concern about increased exchanges between Russia and the North, and the allies have stepped up military drills together with Japan in response to the threat from North Korea.
South Korea is calling for Russia to comply with United Nations resolutions in its exchanges with North Korea, a South Korean foreign ministry spokesperson told a briefing on Thursday. (Reporting by Soo-hyang Choi and Jack Kim; additional reporting by Ju-min Park Editing by Sandra Maler, Ed Davies, Gerry Doyle and Gareth Jones)